The scale of semiconductor integrated circuits including logic circuits has increased year by year. Integrated circuits were constituted by several elements at an early stage of development; nowadays, there are central processing units (CPUs) and digital signal processors (DSPs) constituted by tens of millions of elements. Although power consumption per element is reduced by miniaturization and reduction in voltage of elements, power consumption of the entire integrated circuit is being increased because the number of elements is more increased. As a method for reducing power consumption, clock gating by which clocks are partly stopped, a method for lowering the clock frequency, and a method for lowering power supply voltage partly have been developed.
Power consumption includes static power due to leakage current of an element such as a transistor in the off state, as well as dynamic power due to charge and discharge caused by switching of the element. The static power can be almost negligible in integrated circuits including a small number of elements, but is too large to ignore in integrated circuits including an enormous number of elements. In view of this, a method for controlling supply of power supply voltage to a circuit included in an integrated circuit (power gating) has been developed. Such a method can reduce power consumption due to leakage current.
For example, Patent Document 1 discloses a semiconductor integrated circuit that can implement power gating. Specifically, Patent Document 1 discloses a semiconductor integrated circuit that includes a transistor between a logic circuit and a power supply line, and can control supply of power supply voltage to the logic circuit by controlling switching of the transistor.